1. Field of the Invention
The present invention relates to an optical coordinate input apparatus for outputting an error signal when any one of light emitting element arrays and light receiving element arrays is covered with an insect, mud, or electronically broken down.
2. Description of the Prior Art
In general, an optical coordinate input apparatus is arranged in front of an image display device such as a CRT (cathode-ray-tube) display and an LCD (liquid crystal diode), and employed to input coordinates into a microcomputer. Such an optical coordinate input apparatus is arranged as follows. Light emitting element arrays are positioned opposite to light receiving element arrays in an X-axis direction and a Y-axis direction at a peripheral portion of a screen of an CRT display or the like. These light emitting elements and light receiving elements are sequentially and selectively driven and scanned by way of a multiplexer means. Then, when optical signals output from the light emitting elements which are driven and scanned, cannot be received by the light receiving elements positioned opposite to the light emitting elements due to the fact that the optical signals are interrupted by a finger or the like as a coordinate input operation, a coordinate signal representative of the position where this optical signal is interrupted, is output and then a coordinate input can be obtained by a microcomputer or the like by way of calculation processing.
As a result, when the coordinate input operation by way of a finger or the like is performed, the specific coordinate inputs in the X-Y coordinate system can be obtained by executing the calculation by the microcomputer based upon the coordinate signals in the respective X-axis direction and Y-axis direction in such a manner that the optical signals in both the X-axis and Y-axis directions are interrupted. If any one of these light emitting element array and light receiving element array in either X-axis or Y-axis direction is covered with an insect or mud, otherwise electronically broken down, only one coordinate signal is output and thus, the microprocessor will judge occurrence of an error.
In the conventional optical coordinate input apparatus, if the plane where the light emitting element arrays and the light receiving element arrays are arranged in the respective X-axis and Y-axis directions, is coincident with the Z-axis direction, both the optical signals in the X-axis and Y-axis directions are interrupted by an insect having a short body length. As a consequence, there is a risk that the microcomputer will judge the normal coordinate input operation under this condition.
To avoid such a conventional drawback, the plane where the light emitting element arrays and light receiving element arrays are arranged, is arranged with having positional shifts of the X-axis and Y-axis directions with respect to the Z-axis direction. Accordingly, both the optical signals in the X-axis and Y-axis directions are not interrupted by an insect or the like having a short body length. Such a conventional optical coordinate input apparatus is disclosed in Japanese patent KOKAI (Disclosure) No. 57-139606 (1982).
When any one of the optical signals in the X-axis direction or Y-axis direction is interrupted in the above-described conventional optical coordinate input apparatus, occurrence of an error is judged by properly processing the coordinate signals in the microcomputer. As described above, since the microcomputer is also utilized so as to judge the occurrence of an error, there is another drawback that the throughput of the microcomputer is deteriorated under the condition that this microcomputer is utilized for controlling the operations of other controlling devices.